Survey Results for Greece - area G1: North Aegean Sea
In the 63 hauls effected in the Northern Aegean Sea during Medits-GR197 survey, 202 species were sampled and recognized until today. From these, there were recognized 141 species of fishes, 28 species of cephalopods and 32 species of crustaceans.
The most abundant species (in biomass) in the Northern Aegean Sea were small pelagic species as Engraulis encrasicolus and Sardina pilchardus fished in coastal areas on their feeding grounds. Strictly demersal abundant species were Merluccius merluccius, Lophius budegassa, Eledone cirrhosa, Raja clavata, Parapenaeus longirostris, Scyliorhinus canicula, Lophius piscatorius, Phycis blennoides and Argentina sphyraena. Other semi-demersal or migratory species like Illex coindetii, Micromesistius poutassou and Trachurus mediterraneus gave the most variable quantities.
A more detailed analysis of the results concerning the target species is given below.
This species was present at depths from 10 to 200 m and absent in deeper waters. It has a biomass index (13,22 kg/kmē) and density (530 Ind/kmē) which are higher than the one of Medits 96 (9,07 kg/kmē), in this zone. The maximum length of individuals was 256 mm, whereas the minimum 67 mm. Male individuals were the 37,23% of the total catches, females were 42,91%, while the rest 19,86% were immature individuals.
In general it was found a small biomass index (0,34 kg/kmē), lower even than last year (1,56 kg/kmē) and a low density index (6 Ind/kmē) at the zone of 10-200 m, while it is not fished at all after the depth of 200 m. The minimum length of individuals was 55 mm whereas the maximum 211 mm. Male individuals were the 22,22% of the total catches, females were also 16,67%, while the rest 61,11% were immature ones. The percentages encountered shown that mainly we fished the species in their nursery grounds
It was absent in depths less than 100 m, appeared mainly in greater depths, while the highest biomass index (5,16 kg/kmē) was obtained at the zone of 200-800 m. Different distribution was shown on 96 survey having no presence in the zone 10-200 m and in deeper waters the index was lower (1,98 kg/kmē). Male individuals were the 27,59% of the total catches, females were 40,23%, while the rest 32,18% were immature ones. The immature individuals fished in small numbers were present in the whole sampled zone. The maximum length of individuals was 313 mm and the minimum 38 mm.
Mainly found in depths greater than 100 m, with highest values (7,50 kg/kmē) calculated for the zone 200-800 m, as well as the density index (134 Ind/kmē). The indices calculated for the Medits 96 were similar as those found this year. The maximum length of individuals was 365 mm and the minimum 56 mm. Females were the 37,37%, male ones were the 43,52% while the rest 18,68% were immature.
It is the second most abundant in weight, from the 31 target species in the region of Northern Aegean Sea, present in the entire fished zone The highest biomass index (48,63 kg/kmē) and density index (119 Ind/kmē) was found at depths between 10 - 200 m. This pattern of distribution is not different to that of the 96 survey, where the highest biomass index found was (59,99 kg/kmē) at the same zone. The maximum length of individuals was 630 mm whereas the minimum 49 mm. Male individuals were the 48,65% of the total catches, females were 36,15%, while the rest 15,20% were immature individuals.
Species distributed mainly at the zone 200 - 500, with the highest biomass (21,58 kg/kmē) and density (5 Ind/kmē) indices obtained at depths between 200 - 800 m. The highest biomass index found on Medits 96 was 16,16 kg/kmē at the same zone. The maximum length of individuals was 1200 mm whereas the minimum 142 mm. Male individuals were the 38,89% of the total, female individuals were 55,56%, while the rest 5,55% were immature.
The most abundant in weight of all target species, it was present at all depths. Highly increased biomass index (54,37 kg/kmē) was observed compared to that of previous year (26,29 kg/kmē) and even greater compared to that of Medits 95 (11,66 kg/kmē). The highest value of biomass index (71,17 kg/kmē) was obtained at the zone of 200-800 m as last year, while the highest density index (463 Ind/kmē) was found at 10 - 200 m, where the nursery of small individuals and the feeding ground of immature young fish was localized. The maximum length of individuals was 860 mm whereas the minimum 49 mm. Male were the 24,36% of the total, female were 36,88%, while the rest 39,36% were immature individuals.
It is the third most abundant in weight and the fifth in number, biomass index (23,62 kg/kmē) and density index (338 Ind/kmē) respectively, from the 31 target species at North Aegean Sea. It is present at depths between 100-800 m, with the highest biomass index (35,25 kg/kmē) and density (465 Ind/kmē) at the zone of 200-800 m. When comparing present results to those of the previous year (58,18 kg/kmē total abundance index and 86,46 kg/kmē zone index respectively), we find a significant decrease of the biomass index, but compared with that of 1995, (18,80 kg/kmē), it presents only a slight increase. The migratory behaviour of this species and the resulting catch at random on moving fish schools give reasons for the variable abundance indexes. The maximum length of individuals was 380 mm and the minimum 83 mm. Male individuals were 39,56% of the total number, female were 37,23%, while 23,21% were immature.
A species abundant at depths less than 200 m, while absent at greater depths. It has total biomass index (10,03 kg/kmē) and total density index (338 Ind/kmē). At depths from 10 - 200 m the values of these indices were (20,74 kg/kmē) and (613 Ind/kmē) respectively. The highest value for this species on 96, appears also at the same zone (21,41 kg/kmē) and it was of the same magnitude. Size of individuals ranged from 102 to 243 mm, from which the 49,54% were male, the 50,46% female.
This species has been found in low quantities at depths shallower than 500 m, with the maximum value (3,53 kg/kmē) obtained at the depth zone of 10 - 200 m. Last year this species was much more abundant. Its biomass index at the zone of 10 - 200 m was more than double, having a value of 7,11 kg/kmē. Size of individuals ranged from 130 to 230 mm, from which 67,86% were male and 32,14% female.
Low biomass index (1,48 kg/kmē) and few specimens equally distributed at all depths in the zone from 10 to 200 m characterized this species . Absent at 500-800 m, whereas in the survey of 96 it was present even in low densities (0,32 kg/kmē). The size of individuals ranged from 138 to 169 mm. The 69,44% were male and 30,56% female.
A species found in low quantities (biomass index 3,42 kg/kmē) in all strata, except in the shallowest zone (10-50 m zone). The distribution pattern and values found on Medits 96 were smaller. The biomass indices were (0,01 kg/kmē) for the depth 10-200 m and (0,32 kg/kmē) for the depth 200-800 m. Size of individuals ranged from 125 to 238 mm and the 54,46% were male, 20,30% female and 25,74% immature specimens.
Appeared only at depths less than 200 m, with value of the biomass index (21,56 kg/kmē) at the zone of 10-200 m and total biomass index (10,42 kg/kmē). A similar distribution pattern was shown last year but with much lower values (total biomass index 3,46 kg/kmē and 7,15 kg/kmē in the zone 10-200 m). Size of individuals ranged from 80 to 357 mm. A clear predominance of female individuals was observed (85,35%), while the males were 13,64% and the immature ones were 1,01%.
Present at all depths except between 10-50 m. It shows low biomass index in shallow waters until the depth of 200 m. Abundant in depths from 200 to 800. The highest biomass index (24,52 kg/kmē) was calculated in that zone. We have found the same pattern of distribution in 96, but its biomass indices (11,09 kg/kmē) were less than the half of this year. Size of individuals ranged from 54 to 557 mm, from which 22,01% were male, 28,46% female and 49,53% were immature. The young specimens were found mainly at depths ranging from 350 to 450 m.
It is the fifth most abundant in weight from the 31 target species at the region of the Northern Aegean Sea. A decrease of the biomass index level (29,45 kg/kmē) of this species was noted compared to these of Medits 96 (36,62 kg/kmē), but remain a significant increase compared to those found in 1995 (19,95 kg/kmē). Generally abundant at depths 10-500 m with the highest biomass index (51,42 kg/kmē) obtained at the zone of 10 -200 m. Size of individuals ranged from 121 to 805 mm, with 54,82% females 43,98% males and 1,20% immature ones.
Present only at depths 10-100 m, absent at greater depths. It has shown extremely low total biomass index (0,60 kg/kmē) and even in the zone 10 - 200 m it shows particularly low biomass index (1,25 kg/kmē). Decreased biomass indices compared to Medits 95 (4.58 kg/kmē) and Medits 96 (3,16 kg/kmē) were observed.
It is the seventh more dense in number of individuals of the 31 target species. This species was abundant at depths less than 200 m. Almost stable biomass index (14,32 kg/kmē) compared to 1996 (14.00 kg/kmē), but increased slightly compared to biomass index levels of Medits 95 (10.10 kg/kmē). The highest indices (29,61 kg/kmē) and (865 Ind/kmē) were observed at depths from 10 to 200 m. Size of individuals ranged from 94 to 192 mm, from which 66,08% were male, and 33,92% female.
It is the second more dense in number of individuals of the 31 target species (1857 Ind/kmē). Abundant at depths less than 200 m . The highest density index (3838 Ind/kmē) and biomass index (62,79 kg/kmē) occurred at depths 10 - 200 m. There exists a significant difference of the biomass index level compared to the value found on Medits 96 in the same zone (11,11 kg/kmē). The migratory behaviour and the particular distribution pattern of that fish explain probably the differences between years. Sizes ranged between 55 and 441 mm. The 47,96% was male, the 39,03% was female and the 13,01% was immature.
It was present at all depths except of 500-800 m. It is the forth more dense in number of individuals species. Especially present at depths between 50 - 100 m, with the highest density index (1143 Ind/kmē) and the highest biomass index (13,11 kg/kmē) at the zone 10 - 200 m. while last year showed higher biomass index levels (29,92 kg/kmē). Size of individuals ranged from 46 to 302 mm, from which 5,87% were male, 9,09% female and 85,04% were immature. The nursery ground of that species located in the shallowest zone, explain the high percentage of young individuals.
The third most abundant in number (651 Ind/kmē) of the 31 target species. It is present at all depths, except 500-800 m. Especially present at depths from 50 to 200 m. The maximum biomass index (17,24 kg/kmē) was observed in the zone 10 - 200 m. In the same zone it has the highest density index (1289 Ind/kmē). On Medits 96 we have found the same pattern but the biomass indices were more than three times higher,(27,10 kg/kmē the total one and 55,05 kg/kmē in the depth zone 10-200 m. Size of individuals ranged from 26 to 208 mm, from which 18,30% were male, 20,21% female and 61,49% were immature, a percentage due mainly to the collection of young individuals.
This species was found in depths from 10 to 500 m, although more abundant from 100 to 200 m. The highest biomass index (18,19 kg/kmē) was obtained in the zone 10 - 200 m. Similar pattern and indices were also shown during the cruise of 96. The maximum length of individuals was 530 mm and the minimum 42 mm. Male individuals were 29,41% of the total number, female were 40,06%, while 23,53% were immature.
Not found at all in our region during the cruises of Medits 96 and 97.
This species was found in extremely low biomass index (0,50 kg/kmē) at the zone of 500-800 m. Even lower biomass index levels (0,02 kg/kmē), practically one specimen, were observed at the same depth, last year.
Low biomass index (0,75 kg/kmē) in shallow waters and higher values (11,54 kg/kmē) were observed in the zone 200-800 m. Some of the specimens were very big (up to 94 mm carapace length) found at depth 400 - 450 m. A similar pattern was also found in the 96 survey, but with different biomass indices levels (1,04 kg/kmē and 7,88 kg/kmē) in the depth zones of 10-200 and 200-800 m respectively. The minimum length of individuals was 16 mm, whereas the maximum 94 mm. 49,28% of the individuals were found to be females, 50,54% males and 0,18% immature.
It is the most abundant of all target species in number (2701 Ind/kmē) and the most abundant in weight from the 4 target crustacean species of the Northern Aegean Sea, having a total biomass index of 24,93 kg/kmē. This species presented the same characteristics with lower biomass indices of 18,47 kg/kmē and 22,56 kg/kmē but higher density indices (2927 Ind/kmē) in 1996 Medits survey, in our region. The high abundance of this species was repeatedly detected during last 3 years in the entire North Aegean Sea and the species offers a good income to the commercial trawlers. It was generally fished in depths from 50 to 500 m, however the maximum of its biomass (29,52 kg/kmē) and density (3543 Ind/kmē) indices was observed in the zone 10 - 200 m. The minimum carapace length of individuals was 8 mm, whereas the maximum 47 mm. 60,32% of the individuals were found to be females, 38,69% males and 0,99% immature.
It was the most abundant from the 5 target cephalopods species of the Northern Aegean Sea. Generally present in depths between 10-500 m. The highest biomass index (39,68 kg/kmē) was obtained in the stratum 10-200 m. The total biomass index level of this species decreased from 13,93 kg/kmē at Medits 95 to 7,55 kg/kmē in 1996 and increased greatly this year to 27,28 kg/kmē. The minimum length of individuals was 12 mm, whereas the maximum 197 mm. 51,59% of the individuals were found to be females, 36,82% males and 11,59% immature.
Fished in shallow waters. Present only at depths 10-100 m, absent at greater depths. It has shown relatively low biomass index (6,17 kg/kmē), even in the zone 10 - 200 m. The minimum length of individuals was 30 mm, whereas the maximum 120 mm. 50% of the individuals were found to be females, 41,67% males and 8,33% immature.
It was the second most abundant from the 5 target cephalopods species of the Northern Aegean Sea, having a total biomass index level of 11,66 kg/kmē and a density of 122 Ind/kmē. This species was fished at all depths, however it was more abundant in the stratum 200 - 500 m. The highest biomass index (12,48 kg/kmē) was obtained in the zone 200-800 m. In the same zone the biomass index (28,45 kg/kmē) observed last year, was more than double. Sizes ranged from 32 to 244 mm, with 24% female individuals, 54,11% male and 21,89% immature ones.
This year it was present from 10 to 500 m increasing depth limits in contrast with the last year sampling, when its presence in our region was limited in the 10 - 50 m depth stratum. The biomass index was low (0,134 kg/kmē) but in any case it is higher from that corresponding of Medits 96 (0,04 kg/kmē).
In the 96 survey it was the second most abundant cephalopod target species of the Northern Aegean Sea, having a mean biomass index level of 18.25 kg/kmē. It was found down to 500 m with the higher biomass index in shallow waters. The maximum biomass index (36,83 kg/kmē) was observed between 10 and 200 m. Minimum length was found to be 30 mm and maximum 220 mm. This year it was found down to 500 m too, with the highest biomass index (19,56 kg/kmē) observed in the same zone. Minimum length was found to be 27 mm and maximum 170 mm. With 57,58% female individuals, 36,36% male and 6,06% immature ones. A new fishing trap, very common along the coast of Thracian Sea affected greatly the quantities fished and the species abundance.
Fished only in the depth zone 10 - 200 m, where its biomass index is relatively low (1,20 kg/kmē). This species was found in low quantities, but more abundant than last year.
Non-targeted species. It was the most abundant in weight (203,76 kg/kmē) and in number (18999 Ind/kmē) species fished in Northern Aegean Sea. It was fished in all coastal hauls (22 of 63 hauls), mainly at the Thracian Sea (upper part of N. Aegean). This species was found in depths between 10-200 m but it was absent at deeper waters. The pattern of distribution shows a peak at the first stratum 50 - 100 m, decreases in abundance at the stratum 100-200 m and low abundance at the depth of 10 - 50 m. The observed biomass index in the zone 10 - 200 m was (421,39 kg/kmē). In the same zone it has high density index (39290 Ind/kmē). Sizes ranged from 84 to 156 mm, with 45,24% female individuals, 46,17% males and 8,59% immature ones. Comparing the results of two surveys (1996-1997) we found a great similarity in the distribution pattern of the species in both surveys. Last year we had fished anchovy in 17 hauls. The total catch was 364,1 kg and this year it was 784,1 kg and the total number was 31714 and 74839 individual respectively. The mean weight of the specimens is 1 gr. lower this year.
Very abundant in fishing grounds along the coast. It was the second most abundant, in kg (105,75 kg/kmē) species fished in Northern Aegean Sea and the third most abundant fish in numbers (4593 Ind/kmē). It was found at 25 out of 63 hauls during the Medits-97 in our area. It was fished in the depth zone 10 to 200 m with biomass index (218,70 kg/kmē) and dense index (9499 Ind/kmē). The higher quantity was fished at the stratum 50 - 100 m, showing a slight decrease at the 10 - 50 m depth stratum. The minimum length of individuals was 62 mm, whereas the maximum 195 mm. 33,34% of the individuals were found to be females, 55,32% males and 11,34% immature. Comparing these data with the data of Medits 96 we find a great similarity in the distribution pattern of the species in both surveys. Last year we had fished sardine in 18 hauls.. The mean weight of the specimens was 18,29 gr. last year and 23,01 gr. in this year. In one haul of the 97 survey we have fished about 60 kg of small fish, the mean weight of which was 4,26 gr.
This depth zone includes the highest proportion of the target species (29 out of 31). From the crustaceans two species (N. norvegicus and P. longirostris) appeared. All target species of cephalopods were present.
A general increase in biomass index of the target species was observed during the 97 survey compared with the Medits-GR 96. The most abundant species were Trachurus mediterraneus (62,79 kg/kmē), Raja clavata (51,42 kg/kmē) and Lophius budegassa (48,63 kg/kmē). A high biomass index of Eledone cirrhosa (39,68 kg/kmē), Merluccius merluccius (36,43 kg/kmē), Spicara flexuosa (29,61 kg/kmē) and Parapenaeus longirostris (29.52 kg/kmē) was observed. Finally, the higher density indices were observed for Trachurus mediterraneus (3838 Ind/kmē), Parapenaeus longirostris (3543 Ind/kmē), Trisopterus minutus capelanus (1289 Ind/kmē) and Trachurus trachurus (1143 Ind/kmē).
22 of the target species were found in this stratum included three species of crustaceans (A. foliacea, N. norvegicus and P. longirostris) and five of the six species of cephalopods (Eledone cirrhosa, Illex coindetii, Loligo vulgaris, Octopus vulgaris and Sepia officinalis). Merluccius merluccius (71,17 kg/kmē) was the dominant species in this depth zone, whereas Micromesistius poutassou (35,25 kg/kmē), Phycis blennoides (24,52 kg/kmē), Lophius piscatorius (21,58 kg/kmē) and Parapenaeus longirostris (20,62 kg/kmē) were also abundant. Finally, a high density index (1912 Ind/kmē) of Parapenaeus longirostris was observed.
The global analysis of the data for the Northern Aegean Sea, irrespective of depth zones, shows that the most abundant in weight fish target species are the following: M. merluccius (54,37 kg/kmē), L. budegassa (32,32 kg/kmē), T. mediterraneus (32,32 kg/kmē), R. clavata (29,45 kg/kmē) and M. poutassou (23,62 kg/kmē). Furthermore, the most abundant in number fish target species are: T. mediterraneus (1857 Ind/kmē), T. minutus capelanus (651 Ind/kmē), T. trachurus (557 Ind/kmē), S. flexuosa (418 Ind/kmē), M. merluccius (378 Ind/kmē), M. poutassou (338 Ind/kmē) and M. barbatus (296 Ind/kmē).
The most abundant in weight and in number of the four crustacean target species are: P. longirostris (24,93 kg/kmē and 2701 Ind/kmē) and N. norvegicus (6,32 kg/kmē and 128 Ind/kmē), respectively.
From the six cephalopods species, more abundant were found to be E. cirrhosa (27,28 kg/kmē and 130 Ind/kmē) and I. coindetii (11,66 kg/kmē and 122 Ind/kmē).
In general, when comparing the two surveys it is found that 15 target species presented higher and 10 lower total biomass indices on 97, whereas 4 remain stable. The most significant differences have been noted in: M. merluccius (26,29 kg/kmē and 54,37 kg/kmē respectively), T. mediterraneus (5,38 kg/kmē, 31,31 kg/kmē), E. cirrhosa (7,55 kg/kmē, 27,28 kg/kmē), T. trachurus (14,67 kg/kmē, 6,48 kg/kmē) and T. minutus capelanus (27,10 kg/kmē, 8,66 kg/kmē), on 96 and on 97 respectively.